On Tue, Oct 15, 2019 at 10:30:08AM +0200, Peter Zijlstra wrote: > On Mon, Oct 14, 2019 at 01:03:08PM -0400, Joel Fernandes (Google) wrote: > > In current mainline, the degree of access to perf_event_open(2) system > > call depends on the perf_event_paranoid sysctl. This has a number of > > limitations: > > > > 1. The sysctl is only a single value. Many types of accesses are controlled > > based on the single value thus making the control very limited and > > coarse grained. > > 2. The sysctl is global, so if the sysctl is changed, then that means > > all processes get access to perf_event_open(2) opening the door to > > security issues. > > > > This patch adds LSM and SELinux access checking which will be used in > > Android to access perf_event_open(2) for the purposes of attaching BPF > > programs to tracepoints, perf profiling and other operations from > > userspace. These operations are intended for production systems. > > > > 5 new LSM hooks are added: > > 1. perf_event_open: This controls access during the perf_event_open(2) > > syscall itself. The hook is called from all the places that the > > perf_event_paranoid sysctl is checked to keep it consistent with the > > systctl. The hook gets passed a 'type' argument which controls CPU, > > kernel and tracepoint accesses (in this context, CPU, kernel and > > tracepoint have the same semantics as the perf_event_paranoid sysctl). > > Additionally, I added an 'open' type which is similar to > > perf_event_paranoid sysctl == 3 patch carried in Android and several other > > distros but was rejected in mainline [1] in 2016. > > > > 2. perf_event_alloc: This allocates a new security object for the event > > which stores the current SID within the event. It will be useful when > > the perf event's FD is passed through IPC to another process which may > > try to read the FD. Appropriate security checks will limit access. > > > > 3. perf_event_free: Called when the event is closed. > > > > 4. perf_event_read: Called from the read(2) and mmap(2) syscalls for the event. > > > > 5. perf_event_write: Called from the ioctl(2) syscalls for the event. > > > > [1] https://lwn.net/Articles/696240/ > > > > Since Peter had suggest LSM hooks in 2016 [1], I am adding his > > Suggested-by tag below. > > Thanks, I've queued the patch! Thanks! > > To use this patch, we set the perf_event_paranoid sysctl to -1 and then > > apply selinux checking as appropriate (default deny everything, and then > > add policy rules to give access to domains that need it). In the future > > we can remove the perf_event_paranoid sysctl altogether. > > This I'm not sure about; the sysctl is only redundant when you actually > use a security thingy, not everyone is. I always find them things to be > mightily unfriendly. Right. I was just stating the above for the folks who use the security controls. thanks, - Joel
